Problem: Luis has taken 6 tests and his average score so far is 88. If he gets 100, a perfect score, on the remaining 2 tests, what will his new average be?
Solution: If he gets 100 on the remaining tests, the sum of his scores will be $6 \cdot 88 + 2 \cdot 100 = 728$ His overall average will then be $728 \div 8 = 91$.